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PH-EP-2014-008

(Submitted on 27 Jan 2014)

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Abstract

The lifetime of the $B_c^+$ meson is measured using semileptonic decays
having a $J\!/\!\psi$ meson and a muon in the final state. The data,
corresponding to an integrated luminosity of $2\mathrm{ fb^{-1}}$, are
collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of
$8\,\mathrm{TeV}$. The measured lifetime is $$\tau = 509 \pm 8 \pm 12
\mathrm{ fs},$$ where the first uncertainty is statistical and the second is
systematic.

Result of a fit in the ($\mathrm{DLL} _{p/\pi}, \mathrm{DLL} _{K/\pi}$) plane to determine
the fractions of hadron species in the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -track sample.
The colour of each bin is built as
a combination of red, green and blue proportional to the fitted fractions
of pions, kaons and protons, respectively.

Dimuon mass distribution for the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ candidates. The selected
signal region is shown by the central light-shaded area. The sidebands
used for the estimation of the fake $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ background are shown by the
dark-shaded areas, and the function modelling such background by the solid
red curve.

Result of the two-dimensional fit of the $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \mu ^+ \nu _\mu X$ model.
Projections of the total fit function and its components are shown for
(a) the pseudo-proper time , (b) the mass of all events, and (c) the mass of the detached events ($ t_{\mathrm{ps}} > 150$ fs).

Tables and captions

File LHCb-PAPER-2013-063-supplementary.zip contains the following figures:
SupplementaryFig1 : Comparison of the result of this determination of the B_c^+ meson lifetime with those from previous measurements
SupplementaryFig2a : Result of the two-dimensional fit of the B_c^+ -> J/psi mu^+ nu X model -- Time projection
SupplementaryFig2b : Result of the two-dimensional fit of the B_c^+ -> J/psi mu^+ nu X model -- Mass projection
SupplementaryFig2c : Result of the two-dimensional fit of the B_c^+ -> J/psi mu^+ nu X model -- Mass projection for t_ps > 150 fs
SupplementaryFig3 : Mass projection of the model for t_ps > 150 fs after applying a signal deformation which maximise compatibility with data